There is a somewhat surprising phenomenon where perfectly good mothers experience an adolescent child wanting to go live with their dad. I have had many of these mothers in my office. They report that their child has told them that they feel their childhood years are coming to a close and they want to spend a little of that time in the custody of their father. In their young, but surprisingly astute minds, they have calculated that precious years that can never be regained are about to be lost. You can also add to this phenomena the Dad thinking the same thing and wooing the child over to his side with gifts and new-found attention. This phenomenon is so prevalent that I have built a warning about it into my exit interview. I am not sure what a mother can do about it, other than maybe be sensitive to it and prepare to handle it in a way which does not make the child resentful.